This invention relates to electronic circuit cards and their use in a system having one or more card sockets wired to a host device, particularly to small encapsulated cards containing significant amounts of re-writeable non-volatile memory such as flash EEPROM (electrically erasable and programmable read-only-memory) and the system in which they operate when removably inserted into multiple card sockets.
Small cards containing non-volatile semiconductor flash EEPROM systems have become popular for storing multiple megabytes of data from personal computers, notebook computers, personal electronic assistants, cellular telephones, cameras and other electronic devices requiring removable data storage. The applications of such memory cards are increasing rapidly, currently being used to store music downloaded from the Internet. Music data is normally transmitted over the Internet in a compressed form, such as by a well known MP-3 algorithm, and stored in the compressed form on a card for later decompression and reproduction on an analog playing device. Very small battery powered portable players with a memory card slot (socket) are beginning popular. The use of such cards to store and transfer video and other high capacity data is likely in the future as the bandwidth of the Internet and connections thereto increase, as the storage capacity of the memory cards increases and as the efficiency of data compression algorithms increases.
A card that is especially adapted for these and other applications is the MultiMediaCard (xe2x80x9cMMCxe2x80x9d) that is only 32 millimeters long, 24 millimeters wide and 1.4 millimeters thick. The physical and electrical specifications for the MMC are given in xe2x80x9cThe MultiMediaCard System Specificationxe2x80x9d that is updated and published from time-to-time by the MultiMediaCard Association (xe2x80x9cMMCAxe2x80x9d) of Cupertino, California. Versions 2.11 and 2.2 of that Specification, dated June 1999 and January 2000, respectively, are expressly incorporated herein by this reference. MMC products having varying storage capacity up to 64 megabytes in a single card are currently available from SanDisk Corporation of Sunnyvale, Calif., assignee of the present application. These products are described in a xe2x80x9cMultiMediaCard Product Manual,xe2x80x9d Revision 2, dated April 2000, published by SanDisk corporation, which Manual is expressly incorporated herein by this reference. Certain aspects of the electrical operation of the MMC products are also described in co-pending patent applications of Thomas N. Toombs and Micky Holtzman, Ser. Nos. 09/185,649 (now U.S. Pat. No. 6,279,114) and 09/186,064, both filed Nov. 4, 1998, and assigned to SanDisk Corporation. The physical card structure and a method of manufacturing it are described in U.S. Pat. No. 6,040,622, assigned to SanDisk Corporation. Both of these applications and patent are also expressly incorporated herein by this reference.
MMC products have a serial interface that uses only six electrical contacts, one for transfer of data, one for receiving commands and sending responses (status indications), one to receive a clock signal and three to receive power. A spare contact has been included for future use. The few number contacts simplifies the cards"" use with host systems, particularly portable ones, and allows the size of the cards to be reduced. Of course, the rate at which data can be transferred into and out of the card is limited for a given clock frequency by use of a single data contact, as opposed to transferring data in parallel through multiple contacts as done in other larger memory cards having different formats. Host systems often provide two or more sockets for the simultaneous use of two or more MMC products. All the data contacts of multiple inserted memory cards are connected by a single line to the host processor, all the command/response contacts are similarly connected to the host processor by a single line, and all the clock contacts of the cards are connected together to a common clock source.
The host is required, as part of a system initialization routine, to assign a unique address to each card inserted in multiple system sockets. A unique card identification (xe2x80x9cCIDxe2x80x9d) number is stored in a register of each card by its manufacturer in a manner that it can be read by a host but this number has a very large binary size. Since a card""s address either precedes each command, or is included in the argument of others, that is transmitted over a the single command/response line to all cards, for example, the use of a very large address can significantly slow down operation of the multiple card system. Transmission of the long manufacturer""s identification is not necessary for addressing just a few cards used in a typical system. Only 1 bit is needed to address two cards, and two bits for up to 4 cards, for example. Therefore, on initialization, a small relative card address is written into an internal card register that is provided for this purpose, referenced as the relative card address register (xe2x80x9cRCAxe2x80x9d).
In order for the host processor to initially be able to address each card in turn to assign such addresses, the host commands all cards of the system to simultaneously transmit their manufacturer identification codes bit-by-bit until a combination of bits from all the cards results in all but one of the cards becoming inactive. The relative address is then written by the host into the RCA of the one remaining card, and the process is thereafter repeated for the remaining cards until each of the cards is given a unique, small address. These addresses are then subsequently used by the host to individually access the cards in the system. This initialization technique is further disclosed in Patent Cooperation Treaty (xe2x80x9cPCTxe2x80x9d) International Publication No. WO 97/38370 of Siemens Aktiengesellschaft, which publication is expressly incorporated herein by this reference.
It is expected that MMC products having a single card data storage capacity of 128 megabytes will be commercially available in the near future. This higher capacity and much more are currently commercially available in other flash EEPROM cards that are larger that the MMC products. With use of the current MP3 compression algorithm, over one hour of music can be stored on a single 128 megabyte card. And as the storage capacity of such cards increases further, and/or as compression algorithms further reduce the size of data files, music of even longer duration, and other types of digital data, can be stored on individual cards. Because of the many different ways that small non-volatile memory cards are contemplated to be used, it is desirable to maximize the flexibility and efficiency in their structure and use with the Internet, and their use in host systems that have a single card socket, as well as with hosts that have two or more sockets to utilize two or more memory cards at the same time.
A new non-volatile memory card has been developed which, among other improvements, adds electrical contacts to increase the data transfer rate with the card and alters the way in which relative addresses are assigned to each of multiple cards of a system. This new product is called a Secure Digital (xe2x80x9cSDxe2x80x9d) Memory Card, a specific example of a card that implements the various aspects of the present invention. The size and shape of the SD Card are preferably made the same as the MMC in plan view but the thickness of the SD Card can be either the same 1.4 millimeters as the MMC, or may be made to be greater than that of the MMC, an example being 2.1 millimeters with the external contacts of the SD Card being slightly recessed. The SD Card contains additional external electrical contacts but the positions of the other contacts are the same as those of the MMC in order that sockets designed to accept the SD Card will also accept the MMC card. The electrical interface with the SD card is further made to be, for the most part, backward compatible with the MMC product described in version 2.11 of its specification referenced above, in order that few changes to the operation of the host need be made in order to accommodate both types of card.
According to one aspect of the present invention, the host system and cards are modified to cause relative addresses to be assigned to each of multiple SD Cards, or other electronic circuit cards with similar host interfaces, in less time than now required for the MMC products. Specifically, a separate command/response line is connected between the host and each of the card sockets of the system. The host then, during system initialization, controls the assignment of unique relative addresses to the cards by communication between the host and each card over the card""s individual command/response lines. After this initialization, however, all of the socket command/response lines are then connected together so that the host communicates with all cards through a single command/response line in the same manner as the MMC. The MMC thus remains compatible with the SD Card in this aspect of its operation after initialization. The SD Card is simplified by eliminating the open drain circuits that are connected to the command/response contacts of the MMC products. This new technique temporality adapts a system having all card sockets wired to a single common command/response line into a point-to-point communications system for the limited purpose of initializing each card with a relative address that is thereafter used by the host to communicate with the individual cards over the common command/response line. Other techniques to individually address the cards, such as by adding a chip select line to each socket, would require further modifications to the SD Cards and the host interface with them so that the MMC products could thus not be used with the modified system.
According to another aspect of the present invention, the SD Card has two or more data contacts, instead of the single data contact used in the MMC products. Two or more data lines are then included between the host processor and each of the card sockets in order to simultaneously transfer two or more bits of data between the host and an addressed card. Information readable by the host is permanently stored in each card to indicate the number of data contacts of the card. The host then adapts to transfer data between it and that card through all of the available data lines which the card supports. The cards of a multiple card system need not all have the same number of data contacts since the host can transfer data between itself and different cards over different numbers of the common multiple data lines. The modified system can operate with existing MMC products by transferring data over only one of the multiple data lines. This aspect of the invention also has application in systems with a single card socket, since cards with different numbers of data contacts can be interchanged and the host will adapt to a new card by reading its characteristic and configuring the data transfer over all of the system data lines to which the card is connected.
According to a further aspect of the present invention, a serial data stream, such as a one-bit wide stream, is transmitted in parallel through two or more data paths (lines) by alternately directing a fixed number of consecutive data bits at a time, such as one bit, through each of the multiple data lines in sequence, and then reconstructing the data stream from the multiple lines by performing an inverse combination of data bits from the multiple lines. This technique is useful when it is necessary to adapt to a variable number of data lines, particularly when data is being transmitted between a host and a specific memory card over a number of data lines equal to the number of data pins on the card, a number that can vary from one to some multiple such as four. In a specific embodiment, the host adapts to the number of data lines by reading that number from a register in an addressed card before transmission of data begins between the host and that card.
Each of the foregoing aspects maybe utilized alone or they may be combined in an improved electronic card system. The present invention includes combining serial communication between the host and multiple memory cards with point-to-point communication between them in a manner that improves system performance and flexibility, all while maintaining compatibility with an existing system that uses only serial communication between them.
Additional features and advantages of the present invention are included in the following discussion of specific embodiments thereof, which discussion should be taken in conjunction with the accompanying drawings.